By some counts, there are about 40,000 health-related mobile apps available for download on the iPhone, Android devices or other smartphones. The vast majority of these apps exist outside the scope of F.D.A regulation, but mobile health app developers have still been waiting for the agency’s final word on where it plans to focus.

On Monday, the F.D.A. said its oversight will apply to two broad categories of apps:

Those intended to be used as “an accessory to a regulated medical device” – for example, an app that enables a healthcare provider to diagnose a condition by viewing a medical image from a picture archiving or communication system on a smartphone or tablet; or

Apps that “transform a mobile platform into a regulated medical device” – for example, apps that turn smartphones into an electrocardiography (ECG) machine that can detect abnormal heart rhythms or determine if a patient is experiencing a heart attack.

Apps that fall into those categories will be evaluated using the same regulatory standards that the F.D.A. applies to other medical devices. The agency also emphasized that it does not regulate the sale or general consumer use of smartphones or tablets and it said it does not regulate mobile app distributors like Apple’s iTunes App Store or Google’s Play Store.